Is it hard to replace the battery in a RCL 3000 rechargeable lantern?

Pretty much impossible unless you fish it through with a snake wire. You don't say why you are trying to do this? Just use a standalone rechargeable LED light or lantern.

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It looks like it is around 23 years old. Made in China. See if you can send it back for repair :>D

The most likely cause is something not connected during the battery change over. It worked on the battery power when it was installed, but when it ran out, the charging circuit has a break somewhere and is not recharging. Also check the charger for Output Voltage. It is a 12 volt charger

https://fccid.io/NW9-RCL3000R/Test-Report/3000-25688

https://www.google.com/search?q=RCL+3000+remote+control+Lantern

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the Off, 1, or 11 position according to this very bad copy of the manual

https://usermanual.wiki/Sky-City/RCL3000R.manual-2

Reset or recharge?

The battery is held in with 2 lugs push them in and remove battery thks

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Check its battery. It might be weak. Replace it and check.

There are several different models of the Swiss Gear rechargeable lantern. On most though, you can remove the top portion of the lantern and check the lighting element inside. In most cases the elements can be removed and replaced. I have a dual filament lantern and from experience I know that every so often you may have to go buy a replacement light piece. If the lantern has been bumped or even just strapped to the outside of the pack while walking, it's possible for those elements to become loose and need repositioning or replacement so do check that. I'm sure that it should be unlikely your charger is malfunctioning unless you left it plugged in for some very extended period of time, in which case I would say the light would be more likely to burn out. But definitely try that and if that doesn't work the battery pack on the lantern itself may have an issue in which case you can always get a replacement.

There are several options to buy replacement batteries for a Coleman rechargeable lantern, model 5348-700. I just picked up two new batteries from www.1000bulbs.com for $4.87 each plus shipping. ($20.99 for 2 with shipping!) Do a Google search for: ub645f1 6 volt - 4.5 ah - f1 terminal battery for other options

I just searched the web and found that this website sells them for $16.99.
http://www.dutchovencookbooks.com/products/lanterns/remote.html