Hi All. I have had a Mecer 4kW/5kVA inverter with 4x 200Ahr Vision batteries for a few years. I have recently added 3kW of solar and am trying to save as much on my electricity bill as possible. The solar is ample to run the load (Av 750W) during the day as well as charge batteries if required. When solar drops to insignificant values I let the system run of the batteries until 49V and then switch to utility to run load. My system is set to charge from solar only and load priority is also set to solar.

I am finding that the system can run loads until around 9pm before switching back to utility at night and that batteries are charged before 11am every day so available solar is wasted during the day. Hence my reasoning is to add more batteries - specifically another set of 4 Vision 200Ahr. My concern however is the new batteries may cause issues connected in parallel to old batteries. Is it better to try and get a similar set of batteries as mine (there is an option to buy a second hand set that was used in a similar role as mine for same period) or go for the new ones.

Regards Vijen

This subject crops up over and over. The most informed comment I have read is on another forum but does deal with the subject in some detail: https://www.4x4community.co.za/forum/showthread.php/234873-Call-for-comment-Batteries-in-parrallel

Thanks Richard. Still not a positive yes one way or another but different ages of batteries have been connected together without issues according to those posts. I am going to go for the second hand set which is similar age to mine. They came out of a working system which was used to provide power when Eskom load shed so should be in similar condition as mine.

The only thing you need to monitor are shorted cells which will upset the battery voltage.

The easiest way to do this is to use a non contact thermometer. This enables you to quickly determine one that is cooking,,