Twist the battery cover off at the base. I just hold the lantern upside down and twist the square rubberized battery cover counter clockwise. It should pop off with a half turn. Put the batteries in position. Then line up the two red arrows when re-positioning the cover.
I use this lantern with NiMH batteries and it works fine. Specifically, I use the Energizer AA Rechargeable 2200 mAh batteries or the Sanyo Eneloop AA 2000 mAh (I have multiple sets of rechargable batteries which I use for all sorts of things). I also use the AA to D adapters so the batteries will fit. The Sanyos last a little longer; probably because they are better batteries. Obviously, the AA rechargeables don't last as long as D batteries. I also haven't timed how long the lantern lasts with AA rechargables, but my best guess is about 10-15 hours. I hope this helps.
Rayovac has changed the way they rate their lights to conform with ANSI standards. Here is their statement:
"* In 2012 Rayovac adopted the ANSI FL1 standard for measuring light specifications. The standards were developed to help consumers compare technical specs between products. The ANSI FL1 standard indicates the light output for this product is 240 lumens."
So, its the same light that used to claim 300 lumens but now states 240. So a person has to be really careful when comparing and make sure they all are using this ANSI FL1 standard, otherwise its all subjective advertsing.
The bottom of the lantern twists off with a quarter turn. Install 3 D cells. It can be quite frustrating getting the bottom back on the lantern so take your time. Once you have the batteries in, the lantern is fantastic. Great light, rugged construction. It is a shame that they don't put instructions for the battery installation or any thing else for that matter.
I'm guessing the leaking battery acid either corroded a terminal or it's covered with rust to the point it wont conduct electricity. You can try cleaning and inspecting the connections if you like. I wouldn't bother..just get a new one. Make sure you wear gloves. You don't want to get battery acid on your skin.