Batteries

Updated 7-12-06

Keep Your Chassis Batteries Charged

Are your chassis (engine) batteries charged when you are parked and plugged into shore power?

You say, yes of course...are you positive? For sure your RV or House batteries are connected to the charger/inverter when you are plugged into 'shore' power, but your engine or chassis batteries may not be!

Many coach builders do not wire the engine batteries into the charger/inverter for 'shore' power charging, rather relying on the engine alternator to charge them while driving. They have differing reasons for not hooking the batteries together so they can be charged together...most notably the fact that the two different batteries are different type batteries for different jobs.

The Engine/Chassis batteries are auto type batteries for large starting currents and quick recharges. Diesel engines usually have two 'auto' batteries of the same type to provide large starting currents and longer cranking times. These auto batteries now days are usually a sealed type, requiring little maintenance...or "maintenance free". While not totally maintenance free, at least you don't have to worry about water levels in the cells. Keeping the batteries and terminals clean is about all that is required for these batteries. These auto batteries are NOT designed to be deep-cycled and recharged many times. You can only deep-cycle these type batteries a couple dozen times before they go bad. They are designed to deliver high starting currents for short periods of time and be quickly recharged by the engines alternator usually at about 14.6 to 14.8V (different than RV batteries).

However, the RV or 'House' batteries are deep-cycle 'marine' type batteries designed to be deeply discharged (boon docking) with carefully controlled recharging cycles at around 14.2 - 14.4V (different than auto batteries). They can be deep cycled & recharged several hundred times depending on several factors. These RV batteries usually are vented to allow gases (hydrogen) generated during the recharging cycle to escape. These type batteries need regular maintenance to maintain the proper water levels in each cell. Note the water is 'boiled' off during recharging, not the acid, so water is all that needs to be added ...DISTILLED water only please!

Note: There is a new type RV deep-cycle battery called the AGM or Absorbed Glass Matt that IS sealed and IS near maintenance free. Some coach builders are providing these newer type batteries. They are very good, but pretty expensive. Your coach literature should tell you what type batteries you have. For an in-depth article on these new batteries. . .see the Nov. 2004 issue of Motorhome magazine, pg.50.

Assuming you have the conventional lead-acid type batteries, they are most likely NOT hooked together for charging, due to the DIFFERENT charging conditions required. Most charger/inverters are programmed to properly charge deep-cycle batteries, NOT starting batteries.

How can you tell if they are hooked together? While parked and plugged into 'shore' power, your power monitoring system will tell you the voltage of your RV/house batteries.

	If your monitor system has a switch to also tell you the voltage of the engine/chassis batteries...then they are not hooked together.
	If your monitor system only has one position on the volt meter, use an external volt meter and measure the voltage on both sets of batteries. If they are hooked together, they will read about the same voltage. . .if the voltages is significantly different, they are not hooked together.

SUMMARY:

If your RV/Chassis batteries are not hooked together with the Engine/Starter batteries, you may want to consider using an external charger to keep the Engine batteries topped-off while you are parked.

Today's newer motor homes have 2 to 3 slide-outs (even quad slides) plus leveling jacks and are often run from the Engine/Chassis batteries and draw a sizeable load from your batteries.

With no re-charging while parked, your engine batteries will not last as long as you might expect.

Regular Lead-Acid batteries will discharge about 12% per month with no load and no charging.

You can tell if your slide-outs and jacks are run from your Engine batteries by measuring the voltage after you shut the engine off (12.6v to 12.9v or higher), and then again during or after you put your jacks down and your sliders out (12.0 to 12.4 or lower).

Note: Some high-end coaches do have a 'differential monitoring' system that monitors the voltage on both strings of batteries and uses a relay to switch the Inverter/Charger between battery strings to maintain a proper charge on both sets.

SOLUTIONS:

External Tri-state charger - several good brands exist to safely keep your engine batteries charged. This is the solution I recommend. I use a Sears Diehard Tri-state charger. It has an automatic regular mode, a deep cycle mode and a start mode. My external charger, when set on the automatic 2 amp - slow rate will initially go as high as 8 amps, then taper off down to 2 amps, then to zero as it reaches full charge. . .it will top them off quicker than a small trickle charger. It will cycle on/off to keep the engine batteries at full charge. It will not over charge them.

The model no. is 200.713101, however, it is over 5 years old and may not be a current model number. Note - this is not a special charger...it is just a plain ole Sears Diehard Battery charger that has 3 modes...2 amp auto - 10A auto deep cycle - 60amp manual start. I have a convenient compartment next to the batteries where I carry the charger. Since it is portable and not wired in, I remove it occasionally to charge the car batteries when we forget and leave a dome light on all night!

Wired-in trickle chargers - there are a couple commercial products I've heard about like the Trik-L-Start by LSL Products; Echo ~ Charge by Xantrex; and Start_It by Vector Electronics.

The Trik-L-Start connects the engine batteries to the RV batteries with a charge controller in between.

It contains isolation diodes so you can charge the engine batteries, but can't accidentally drain them. The only draw back I saw was a charge current of 5 amps. That will trickle charge the engine batteries, but that will take several hours to bring them to full charge, depending on how drained they were. For more info see the LSL web site -

http://www.lslproducts.com/TLSPage.html for $48.95. Winnebago sells them in their store for around $60. A few owners, early on complained to Winnebago and received one for free. My understanding now is that Winnebago has stopped supplying the unit for free.

Echo ~ Charge - Thanks to Bill Wright and Ray Egan for the links to the Xantrex Echo-Charger info.

Product Features

15 A maximum charge current

Automatically adjusts for 12 or 24 volt battery banks (both battery banks must be the same DC

voltage and battery type)

Automatically switches on/off without affecting the in-house battery bank or over-charging

Uses excess current from the primary charging source

Built-in thermal and over-current circuits

Reverse polarity protection

Easy three wire installation

One year warranty

http://www.xantrex.com/web/id/103/p/docs/pt/20/product.asp

OR

http://www.heartinterface.de/eng/product.php?naam=charge.htm

Start_It by Vector Electronics - stocked at Camping World ~$30

Start-It^® 1.5 amp on-board automatic float charger trickle charges 12V battery as needed and turns off when battery is fully charged. Level indicator shows charging status. Built-in circuit protection guards against overcharging or short circuit. Ideal for cold weather battery maintenance and improved starting performance.

http://www.campingworld.com/browse/skus/index.cfm?skunum=24849&tab=spec

Battery MINDer - is a Charger, Maintainer and Conditioner

BatteryMINDer is a Battery Charger:

Available in 6, 12, 24 and 36 volt models
Amps dependent upon voltage required
Maintenance Free
Deep Cycle – Golf Car, Marine, Solar
Charges SLA/VRLA, AGM and Conventional wet liquid batteries
Polarity reversal / short circuit over temperature protection
Charge indicator shows correct connections plus
'blinks' when battery reaches full charge
Charges any size battery from U-1 up to 8-D
Charge/Maintain up to 4 batteries (of similar type - in parallel)

http://www.batterymart.com/batteryminder.php

If you have info on this or similar products, please send me an email (see below).

Home brew - Some folks have wired their two battery strings together, using diodes and hopefully in-line fuses. . .but I don't recommend you do this. . .

	Wire/cable needs to be big enough to handle the current draw...
	Diodes need to be the right size and wired with the correct polarity...
	In-line fuses should be used for over current protection and need to be sized correctly...
	Wiring your two different battery types together using the house charger/inverter is NOT a good idea as explained above. The two different type batteries have different charging voltages, different internal resistance, different charging rates, etc.
	If it's really hot weather and you choose to run your generator running down the road to cool the coach in addition to your auto A/C, your generator will activate the RV charger to charge the RV batteries AND the engine alternator will be charging the engine batteries. IF you have the two batteries tied together, even with an isolation diode, the engine batteries will be seeing a charge from the engine alternator AND the RV charger/inverter...not good.
	Wiring mistakes, slips, accidental short circuits with wrenches, etc. can cause serious injury, fire or cause a battery to explode! Short circuited batteries will provide an infinite amount of current for a few milliseconds. . .long enough to do serious damage, like melt your wrench, vaporize your wedding ring, maybe explode, splattering sulfuric acid on you and your surroundings...be careful!

Using the MOM or Booster Switch - I recently heard from some readers that he and some friends came up with the idea of 'wedging' closed the Booster or Momentary switch that is used to tie the two battery strings together so the shore power / charger can charge both strings of batteries. Here is an anonymous quote...

"Just read your article about batteries on the CAT RV Club website. I found it to be an excellent source of valuable information and presented at the "Batteries for Dummies" level, which is appropriate for me."

" I have been keeping my batteries charged using a "trick" shared by several friends. Most coaches have a Momentary switch which uses the RV battery power to help the chassis batteries to start the vehicle. This links both systems together, momentarily. I was told to place an object under the spring loaded momentary switch to hold it in the ON position and that will cause the shore power to charge the coach batteries. Gee, maybe that's why I have to change out ALL of my batteries once a year. Ya think??? Any way, thanx for the good info. "

Thanks for the input! I never thought about using the MOM switch but my guess is that you guys are not the first or the last to come up with that idea. Guess we now know why the MOM switch is designed to be Momentary.

Besides needing different charging voltages, cycles, steps, etc. the different types and brands of batteries have different plate construction and therefore different internal plate resistance...this causes parasitic current drain between different type batteries when hooked together.

So, if you left them connected with no shore power, the batteries would 'drain' from one set to the next, depending on which set had the lower internal plate resistance.

During charging, the shore powered inverter/charger is set for charging RV deep cycle batteries at around 14.2 - 14.4V while the engine batteries need a higher voltage around 14.8V to be properly charged.

The same condition applies for mixing battery brands together in any battery application...always use the same brand and the same 'age' batteries in any application, dry or wet.

Bottom line - don't mix different types or brands of batteries in the same circuit.

If you have comments or feedback, send an email to -

Rudy Morris - morrisrc@att.net

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