Lithium battery upgrade

[Off Rez]

I'm sneaking up on a lithium battery upgrade for my TT and have been reading and watching videos as much as I can, but I still have questions.

1) Is a battery isolation manager(BIM) required for a trailer or is that just on motorhomes? If they are for trailers, where do you install them?

2) Would it be better to go with 2 100ah batteries or just a single 200ah? It seems you would have some backup with double 100ah batts but does it introduce potential problems that a single battery solves? It certainly reduces the complexity of the system to just have 1 battery but no redundancy.

Thanks for any help.

[ependydad]

1, no BIM needed.

2, this is buyer's choice but can have impacts on the amp draw of the batteries if you're running an inverter. Check the documentation of the batteries to find out if you get higher draws out of 2 batteries vs. just one.

[Off Rez]

Thank you. The batteries that I am considering have discharge rates equal to the Ah rating. I have a 1500W inverter I plan to install so I'm looking at a minimum of a 200A discharge capability.

[Aussieguy]

12v Inverter at 1500w will draw 125amps Amps = Watts / Voltage
The battery with a 200amp discharge rate can handle the inverter + other typical small loads


be nice to your battery
try not to use things as..... slides and power jacks while inverter is on a high load.


edit added... remember to shut off inverter when not actually needed .
Standby mode can be quite high for some brands of inverter.

[Off Rez]

Good advice, thanks. Another question: I'll use 2/0 guage wire from the battery to the inverter and on the negative side I'll go through a 500A shunt. I believe the shunt should be grounded to the chassis? If so, what guage wire for the ground?

[TitanMike]

Originally Posted by Off Rez

Good advice, thanks. Another question: I'll use 2/0 guage wire from the battery to the inverter and on the negative side I'll go through a 500A shunt. I believe the shunt should be grounded to the chassis? If so, what guage wire for the ground?

The shunt should be connected directly to the battery negative terminal with wire that is large enough to carry the largest load you will run from your battery. 2/0 as you indicated you will be using for the positive connection to the Inverter. The Inverter negative connection should go to the other end of the shunt. As for connection to chassis from the end of shunt NOT connected to battery, it should be at least same size or larger than the current wire connecting battery negative post to frame/chassis. It's just carrying the charging current which will not be greater than max current from Converter/
Charger. Usually #4 Awg is as large as one needs to go, depending on length

[Aussieguy]

just in case you missed it


leave the main negative cable connected at the frame.
the battery end of that negative cable goes to the shunt


The OTHER SIDE of the shunt gets connected to the negative battery post
use same sized negative cable that connects to the frame.



There will also be a small red wire (positive) on the shunt
it needs to be connected to the battery positive (or positive bus bar).

[TitanMike]

Originally Posted by Aussieguy

just in case you missed it


leave the main negative cable connected at the frame.
the battery end of that negative cable goes to the shunt


The OTHER SIDE of the shunt gets connected to the negative battery post
use same sized negative cable that connects to the frame.



There will also be a small red wire (positive) on the shunt
it needs to be connected to the battery positive (or positive bus bar).

Did you miss the part where he's also hooking up an inverter?

Also, LiFePo4 batteries will often draw max current from the converter/charger which often causes voltage drop issues on the original ground wire installed at factory. Ideally, when upgrading to LiFePo4 batteries the wire from converter to battery should be upgraded. Also the ground wires at converter/power center and at battery.

Of course you'll learn this when you upgrade your own batteries to LiFePo4.