I'm running a Battery Tender Jr. http://www.amazon.com/gp/aw/d/B000CITK8S/ref=mp_s_a_1?qid=1360768379&sr=8-1&pi=SL75
If I recall correctly, that one is a 3 stage charger with a true float charge mode. It should not harm a MC battery with continued connection and operation. Exception;see below.
I don't recall if it has a reset feature, which would make it return to peak charge mode after some length of time, or battery voltage monitor trip point. The best battery maintainers have this.
It's a good charger/tender. But, I don't believe it has temperature compensation to adjust the voltage trip points to those changing conditions. As chemical activity changes with temps, a full battery when cold will read a lower voltage than a hot battery. So, chargers often assume the battery being tested/charged at room temperature and deliver voltage based on that norm. This voltage is too high if the battery is left in near freezing temps, and the battery can be overcharged, and the electrolyte "boiled" away.
So, if your tender is being used with a cold battery, better check the electrolyte levels monthly and replenish with distilled water when it gets low. Otherwise, your tender can ruin the battery via electrolyte loss, exposing the plates to oxidation.
Cheers,
