In a previous post I explained my rational for purchasing Firefly batteries in this battery replacement cycle. They arrived a few days ago (finally!) and here are my initial impressions.
Physical fit: They are Group 31 batteries, which is nothing but a specification on the physical size of the battery case, so they should be drop in replacements, right? Wrong! They are a little bit higher than our old Lifeline batteries, so I needed to trim a bit off the wood brace on the bottom of the compartment lid. Also, the terminals are high enough that the battery terminal fuses I had been using no longer fit under the lid, so I swapped four 125 amp terminal fuses for a single 500 amp ANL fuse. Neither was a big deal, but both were annoying.
It is very not fair to evaluate batteries when first installed. Batteries take at least 10 charge/discha rge cycles to settle in to their long term groove. That said...
One of the reasons I went with these was their higher charge acceptance rate. Wow. What a difference. Our Lifeline AGMs (which are very good at rapid charging) would taper down to 18 amps charge rate by the time they got to 85% charge. The Fireflys were still accepting over 50 amps at 85% charge... Once they have settled in and I have a bit more experience with them I'll post more hard data, but so far, they look like they will at least match my expectations.
Again, these are not for everybody. They are expensive, hard to get, and need proper charge voltage control (especially on float) that not every charging system can do. The benefits of the extra cost really depend on how you use your boat.
Fort Lauderdale, FL