I have the LSI 9280-8E Raid controller. The battery is a 3.7VDC 1.4mah Lithium-Ion Battery. The Replacement battery new from LSI (if you can still get it) is upwards of $250. Used from eBay it is about $50 but doesn't guarantee the life of the battery. You would be getting rid of the entire battery module and battery when you replace it. Using my method, you only replace the battery as needed.
I searched for a 3.7VDC Lithium-Ion Battery and found a GoPro Charger and two batteries rated at the exact specs for $18 on amazon. I later found and had suspected before purchasing that the batteries wouldnt be the correct amperage which it was actually just below 1000mAh.
I proceeded to remove the module from the raid controller by removing three screws. holding it on.
I had to cut open the cover/sticker concealing the battery and the board for the battery. NOTE THE POLARITY.
I then found that the charger had a removable battery holder which was convenient. i then opened that with the 4 screws holding it together and removed the existing wires noting the polarity. **BE SURE TO LEAVE THE BATTERY IN**
I then proceeded to solder new wires to the leads and sealed the battery holder after fishing the wires out of the holder to be able to solder to the board of the controller battery module.
After soldering the wires to the leads where the old battery was keeping the earlier noted polarity, i then super glued the battery cradle to the raid battery module which was the exact same width.
The finished product was great. please keep in mind that the battery is significantly thicker on the raid card and may interfere with heat sinks or other cards in the server your using the card in. you may want to relocate the battery elsewhere in the server by leaving the wires longer and not super gluing them together.
overall i think this was nice to re-purpose an otherwise deemed dead piece of tech while future proofing my investment.