THat's right. You've got to have 6V charger. I've been using the one of those little ones with 6V / 12V switch. Worked fine.
I had 6V battery on a bait tank for a long time. It runs forever, it is less noisy... You better keep an eye on the water intake though as the water-flow with 6V seems to stop much easier when you get eelgrass and other crap on your filter...
I don't use it any more as I have a kayank with a timer switch and a 12V battery that powers everything.
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