question

[Barry Morrison]

have built 400 watt system from mobile solar power made easy book with 4 v-max batteries can i add another 400 watt with another charge controller to system .for faster battery charge in winter

 

[MichaelK]

So little information is available that no recommendation can be made. What is your system voltage? What is the charge controller? What is the amp limit of the controller? How are the panels oriented, and how much of their potential capacity is actually produced?

 

[Substrate]

I'm assuming the Vmax Tanks brand of AGM batteries, although I see they also support LiFePO4 now.

If AGM, then get close, but don't exceed their maximum input current ratings with your new array (when you calculate the parallel capacity). Typically 0.25 to 0.3C. Perhaps more. Use a remote temperature probe for more accurate temp compensation. Ideally perform a commissioning charge if you haven't done so, by charging each one individually at least once.