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Old 06-02-2012, 05:04 PM   #2
autostaretx
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Default Re: Adding additional battery

You're probably seeing the effect (consequences?) of too-accurate German engineering.
The normal charging system probably was not designed to handle long-period overloads (i.e. if you want more current, buy the supersized optional alternator).
Let's assume that the charging system can:
(a) easily handle one (the starter) battery at a low state of charge
(b) safely (but perhaps running a bit warm) handle two (one starter, one aux) batteries at fairly low states of charge.

But when you add a third (2nd aux) low battery, you're now running at 3 times the "easy" load, and 50% above the "safe" load.

If you never run your batteries into those "low states of charge", then you'd probably still be safe with two aux batteries.
But if you ever *did* "flatten" the batteries, then you'd be in the risky zone.
And MB would be very unwise to recommend such usage.

One answer would be to have an "intelligent" battery controller between the Sprinter's charger and the battery bank.
Among its duties would be to limit the current demands that charging the batteries puts on the Sprinter.
(thus extending the number of running hours needed to bring the aux batteries up to full charge).
Another set of answers would be a mix of: bigger alternator, perhaps a 2nd alternator, other battery switching systems (perhaps split the battery bank so that only one aux battery is charged at a time? This is similar to the "smart controller" option)

--dick
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