I have a Pro User DC smart battery charger 12v,8amp and recommend 10ah-150ah use.

I want to charge a 200ah gel battery,80% SOC,so it's merely a top up and health check. (I have 4 of these but intend to do one battery at a time)

Is it recommended I use this charger,,although it's smaller or should I invest in a bigger charger?

I reckon that would work just fine as you will only be charging 20Ah per battery and all 4 is well below the 150Ah max, so you can probably do one after the other without it getting too hot. It might just take a little longer as it's only 8A max current, but at top of charge the battery doesn't accept a lot of current anyway.

Thanks for the guidance and info,will give it a try,this was helpful.