Battery question

[Buckman]

We have a100ah AGM battery in rthe caravan which is recharged via the 100w solar panel. The Truma controller for the solar panel is set to AGM.

We have a 110ah Numax lead acid battery in the shed which is about 5 years old, but has hardly been used in the 5 years and this morning was still reading nearly 13v although it has not been recharged for several months.

We have been considering going off grid this summer to one or two CLs. I am not sure whether the batteries can be joined in parallel as they are of a different types. Is it possible?

If not and we purchased another 100ah AGM battery could it be connected in parallel taking into consideration that the battery connected in the caravan will have the solar panel connected to it. I don't want to buy another battery if it cannot be recharged and might as well try and sell the 110ah battery as it si sitting doing nothing.

I was thing of using the caravan battery and then when that gets low connecting up the spare battery so that the caravan battery can be recharged, but without swapping over the batteries.

Alternate is a generator in case there is a lack of no sunny days. Prefer to avoid a genny.

 

[Raywood]

I cannot see any reason why it would not work and the batteries are near enough on capacity. To me the problem may be where the second battery will go as it needs to be in a sealed box vented to the outside. This might cause problems with finding space and fitting. I agree gel batteries are better but they cost a fortune.

 

[Jcloughie]

I believe that connecting in parallel will only drain the better into the poorer battery, I think it’s OK when the charger is connected and providing sufficient potential.

Where will you put battery number 2? If it’s in the boot, you may be able to use the vans control panel to switch between the two. This would require a little rewiring in the car so that the permanent live is connected to batt #2 and not the car, but, with a relay to bring the car battery into parrellel with #2 when the potential is present.

The van battery would still be connected to the solar.

John

 

[Buckman]

Scrap both and buy a pair of new gel ones, connecting those old different batteries up won't end well.
Gels can be discharged lower with no damage, so you might only need one anyway.

The AGM battery is almost new as it came with the caravan and is in perfect condition. I bought the 110ah lead acid in 2015 for a rally and have not really used it since except to charge it up every now and then. It is still in very good condition.

 

[Buckman]

I cannot see any reason why it would not work and the batteries are near enough on capacity. To me the problem may be where the second battery will go as it needs to be in a sealed box vented to the outside. This might cause problems with finding space and fitting. I agree gel batteries are better but they cost a fortune.

The battery will be carried in the vehicle until it is needed.

 

[ProfJohnL]

Different types of battery require differnt charging protocols to fully and safely charge them. Consequently connecting different types of batteries in parallel can cause some problems.

A similar problem can arise even if the two batteries are the same type, but one has a low charge or poor condition.

In some cases the battery with the higher voltage will attempt to discharge into the battery with a lower terminal voltage. This might cause some very high currents to flow between the batteries. In the worst cases this could damage wiring or the battery.

 

[Buckman]

Thanks. Will drop that idea for awhile.

 

[bertieboy1]

We have a100ah AGM battery in rthe caravan which is recharged via the 100w solar panel. The Truma controller for the solar panel is set to AGM.

We have a 110ah Numax lead acid battery in the shed which is about 5 years old, but has hardly been used in the 5 years and this morning was still reading nearly 13v although it has not been recharged for several months.

We have been considering going off grid this summer to one or two CLs. I am not sure whether the batteries can be joined in parallel as they are of a different types. Is it possible?

If not and we purchased another 100ah AGM battery could it be connected in parallel taking into consideration that the battery connected in the caravan will have the solar panel connected to it. I don't want to buy another battery if it cannot be recharged and might as well try and sell the 110ah battery as it si sitting doing nothing.

I was thing of using the caravan battery and then when that gets low connecting up the spare battery so that the caravan battery can be recharged, but without swapping over the batteries.

Alternate is a generator in case there is a lack of no sunny days. Prefer to avoid a genny.

Hi,
Connecting batteries in parallel will increase the Ah capacity 100+110 =210 Ah and the voltage will be nominally 12 Volts,connecting in series doubles the voltage but Ah stays at 100Ah ( the smaller battery)
With the batteries in parallel the solar panel will take roughly twice as long to recharge the batteries.
When discharging the bigger battery will take more current (proportionately 110/100 -1.1 times more current,it all depends on the internal batteries resistances.
As has been said in another post - better for the batteries to have the same characteristics.