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Old 12-31-2017, 08:10 AM   #1
2 Rivet Member
 
2018 25' Flying Cloud
Saint Thomas , Ontario
Join Date: Nov 2017
Posts: 28
Mixed Battery Types on Single Charging Circuit?

Someone once said in times of rapid change experience can be your worst enemy. My past experience is cruising sail & power boats & managing onboard DC & AC systems. My “rapid change” is moving to a new AS, due in February.

My question is: Have you had any issues with mixing battery types on the same charging circuit between your TV and your AS? By “issues” I mean less-than-expected battery life in your AS or TV, alternator problems etc.. By battery “types” I mean lead-acid-starting, lead-acid-deep-cycle, AGM, Lithium.

In the past I have tried to avoid mixing battery types on the same charging circuit. My assumption is different battery types have different charging profiles. This leads me to believe that mixed battery types on a single charging circuit is probably not a good thing, as it would be difficult or impossible for a single charging system to apply the proper charging profile to each battery in the system.

Another thread on the forum re: Lithium batteries is relevant because I think it speaks to the challenges of the TV charging system effectively handling the needs of the TV and the AS (including possible mixed battery types). For example, if the TV system voltage is below that of the AS, the TV can pull power from the AS batteries. To prevent this, some folks are installing relays, diodes, 12V battery distribution boxes while others are disconnecting the TV charging circuit.

Another specific concern is my TV, which is a 2014 VW Touareg TDI. The Touareg battery is an AGM with “Battery Energy Management” designation. The battery is specific to the vehicle, installed inside under the driver’s seat. I understand the vehicle’s Energy Management Control Module “learns” the charging profile of the installed vehicle battery based upon personal use over time and adjusts its alternator output accordingly. As evidence when you install a new battery in a late model Touareg, Q7, Cayenne, you need to have the vehicle encoded to match the new battery BEM specs, otherwise the vehicle will keep using the old “learned” charging profile on the new battery and the new battery may never get a full charge. Without encoding there are reports of new batteries going flat within a very short time.

Pulling these concerns together, I have a Touareg with an AGM battery pulling an AS with as-delivered two lead-acid batteries. Furthermore the Touareg may apply it’s “learned charging profile” to the whole charging circuit of mixed batteries while underway. It would seem to me that this situation may not be good for the batteries in the Touareg, the AS or both.

Absent your input I am inclined to just call it a day and keep the methods of charging the TV and the AS completely separate (i.e. disconnect the power supply from my TV to the AS). Of course I will need solar and/or a genny to enable AS independence. Perhaps I could install AGM’s in the AS to at least harmonize the battery types. However this approach may not solve the potential unknowns of the Touareg’s “learning” profile on the charging circuit, where it must alternatively manage either one or three batteries.

It may turn-out that you experienced folks are in fact having no issues at all. In which case I would be happy to strike these concerns from my list and move-on.

Thanks in advance.
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Old 01-04-2018, 03:34 PM   #2
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1985 31' Excella
st. Paul , mn
Join Date: May 2007
Posts: 116
Too long of a post to simply answer the question .
A battery bank is just a collection of cells , a 12v battery has 6 cells .
When charging properly , most chargers do not , a quality programable charger will have a equalizing charge , depending on the battery bank , this maybe once a month or ?
This is to equalize all cells in the bank --- this can not be done when you have a mix of batteries .
Not only the same brand , but the same model and the same date of manufacture .
Then periodic testing - looking for bad cell .
Any battery bank is only as good as the weakest cell in the bank , in the standard Airstream you 2 - 12v batteries , thats 12 cells to look after .
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