Thread: Fullriver Dual Battery

Please keep us informed on how the LIFEPO4 is going.
I am really interested as I would like to get one.
I take it you are chargiing witha DC/DC charger.
Have you tried it with just a normal duAl battery controller?

BTW I think they are now quoting "pb equivalent" AH which is not really the same and very flattering to LIFEPO4 as they then fall off a cliff. although I am rapt in my Lithium batteries for my Ryobi setup.
Still at $1300 for a 120AH Pb equivalent they are very pricey.

A friend was showing me his tiny Pb jump start thingo at the LR expo which cost $250 and all it was was a little lead acid battery with 2 leads. An equivalent LIFEPO4 motorcycle battery is only about $300-350 and is about 1/2 the weight.
Regards Philip A

Nice work !!

Hi Philip and you can’t use a conventional dual battery isolator because lithium batteries have a much higher settled voltage of around 13.2v to 13.4v.

Whereas a lead acid battery has a maximum settled voltage of 12.7v

Conventional isolators are set up so that when the voltage rises above 13.2v, the isolator will turn on. This turn on voltage is not critical and can be higher, to accommodate the higher settled voltage of a lithium.

The problem comes in when you want the isolator to turn off.

Most isolators, these days, are set to cut-out ( turn off ) at around 12.5v to 12.7v.

These cut-out levels are fine for lead acid batteries because their voltage level drops as the battery discharges and even when the isolator is set to cut-out at 12.5v, a lead acid battery only has to reduce it’s charged state by 10% and the isolator will cut-out.

Lithium batteries maintain a constant settled voltage level of around 13.2v minimum, for 80% of their discharge cycle.

So if the lithium is connected, via a conventional isolator, to the cranking battery, the cranking battery will continuously draw current from the lithium battery because the lithium will always be in a higher state of charge than a lead acid battery.

This current draw is not a massive high current, it is actually quite a low current draw and it will take quite a long time ti discharge the lithium down to 80%.

As a lithium battery reaches it’s 80% discharge state, the discharging MUST STOP or major problems can occur with lithium batteries.

The simplest way and best way to charge lithium batteries while driving, it to use an inverter to power either a Sterling or Promariner battery charger ( these are the ONLY off-the-shelf chargers that can safely charge lithium batteries ) and you can set up to charge with as must as a 60 amp battery charger.

Thanks Drivesafe.
A great reply as always and I actually learned something.
So in addition to the battery you have to buy lots of extra stuff , and a 60 amp ie 700 watt inverter and 60 amp charger will not come cheap or small either!
What if you had a dual battery controller that cut out at 13.4 volts and cut in at 13.9. Most "old style" alternators will start at 14.5 and I guess you could use the resistor trick with newer ones.
Ah well so much for my dreams.
Regards Philip A

Hi again Philip and to be honest, if ( when ) I set up a lithium battery system for myself, I would charge direct from the alternator of any vehicle.

Lithiums are a bit finicky and it’s far safer to charge them in an automotive situation, using and inverter to battery charger type set up.

A simple set up would be to use a standard type isolator to power the inverter.

Job done.

I now have a new twin isolator that is specifically set up for both powering up an inverter or powering a 3 way fridge, while still operating as a standard type isolator, for charging a lead acid auxiliary battery.

The main advantage is that the fridge/inverter control is not activated for 5 minutes after the motor is started.

Good morning
Am in NZ and looking to fit lead acid second battery for touring, running fridge etc. Can you plse tell me which makes and models will fit in the battery compartment of a Puma 90 alongside the factory start battery ? Auto sparkie could not identify one

Originally Posted by Red90Puma

Good morning
Am in NZ and looking to fit lead acid second battery for touring, running fridge etc. Can you plse tell me which makes and models will fit in the battery compartment of a Puma 90 alongside the factory start battery ? Auto sparkie could not identify one

Red90puma,
I fitted a Fullriver 120ah lead acid beside the factory job. But i know that could be a touch large.

Cheers
David