I Think I Just Bought Way Too Much Battery

4gnomad wrote:
Just to follow up on this:

1. Yep, I've got the current L16s in a closet in the front behind the driver's seat.

2. This is a 1994 RoadTrek Versatile with the stock MagnaTek converter/charger. The converter is 32A, but the charger circuit is labeled 15A. I'll have to upgrade to probably a Progressive Dynamics 80A converter/charger. I'll also have to upgrade the wiring on the current 15A circuit to carry that current (this is the part I'm not looking forward to).

3. As someone mentioned (thank you!) apparently I can't just drop in these new batteries as a replacement for the existing marine. Specifically some basic wiring sheets I looked at seem to indicate that there isn't any additional voltage regulation between the alternator and the coach battery so I guess I'll need to add that to ensure my new AGMs don't get overcharged while driving.

You can be assured that you will never overcharge a 400 amp hour battery bank from your alternator charging circuit. If this charge path is not upgraded there's a chance it will blow the fuse or reset-able breaker if the batteries are low and you start driving. Then again maybe not if the wire is too thin, as much factory wiring is especially of that year of conversion.

So you may want to upgrade the wiring to say 2 gauge or larger and fuse it at 100 amps. This wire should go directly to the alternator positive post and then a very short distance later a fuse, because connecting it to the starting battery would have you limited to the fairly small charge wire from the factory charging circuit.

Now, some may argue that this may strain the alternator, and this may be true with your 400 amp battery bank. However, chances are the alternator will only put out 13.6 volts when warm, effectively slowing the charging current. A lot of vehicles have temperature controlled regulation factored into the alternator output as well.

Don't be surprised measuring around 100 amps being output if the van engine is cold and the batteries are low, especially since they are AGM. This could all depend on the power of the alternator as well, could be 75 to 120 amp on a dodge chassis.

So in a nutshell, if you leave the vehicle wiring path alone, chances are it will be inadequate and always undercharge your batteries. Possibly tripping the circuit protection as well if all your connections are good quality and the factory wire isn't micro sized.

If you upgrade your path, fuse at both ends, buy a new solenoid or non diode based isolator, and your alternator may get a workout but your batteries will actually charge.