Adding more house battery

[Happy Hour IV]

I have had 2 series 6 volt golf cart batteries for the house for many years but always a little short after 2-3 days. Misc loads including refrig on inverter. I would like to increase capacity. I have a 80 amp alternator on my genset and 90 amp alternators on my mains so charging when engines are running is not an issue. My batteries are in good condition. I am thinking about adding two more in parallel but the existing batteries are three years old. I have have read about mixing old and new. Any thoughts about this specific application of old and new

 

[bobeast]

Because of the way batteries interact, your new parallel string will never be any stronger than the weakest string. You are effectively doubling the capacity of your weakest battery, when you add a new battery in parallel.

So yes, you will get increased capacity, but not as much as you'd get with all new batteries.

 

[Juliery]

I have had 2 series 6 volt golf cart batteries for the house for many years but always a little short after 2-3 days. Misc loads including refrig on inverter. I would like to increase capacity. I have a 80 amp alternator on my genset and 90 amp alternators on my mains so charging when engines are running is not an issue. My batteries are in good condition. I am thinking about adding two more in parallel but the existing batteries are three years old. I have have read about mixing old and new. Any thoughts about this specific application of old and new

As bobeast says, combining batteries of varied ages is not ideal. It may reduce the service life of the new set and present challenges for correct charging processes. I will suggest you isolate the two sets for both charging and discharging with a switch or VSR. Also upgrade your shore power charger to handle the additional bank.