Two brand new Hitachi BSL1815X Lithium Batteries won't recharge (UC18YGSL charger and DS 18DSAL drill)

These batteries have big problems that Hitachi doesn't address very well. Unlike NiCad batteries, Lith-Ion ones must be periodically used and recharged to retain their battery functions, i.e. if they have been sitting on the shelf at a store for an extended period of time, chances are they will be dead when bought and will not accept a charge. If they go dead i.e. no little red light on the charger when you plug the battery unit in...it's basically junk.

If you can return them or exercise the warranty do so. If / when you get new ones DO NOT completely discharge them like you would NiCads. Lith-Ion batteries do not have the "battery memory" issues that NiCads have which means you don't lose running time if you don't fully discharge the battery unit prior to recharge. Completely discharging before recharge will ultimately kill them. Use the 1815X till almost dead and then charge it. It is also recommended Lith-Ion batteries not be stored fully charged i.e. charge the 1815X fully, drive a couple bolts or screws, remove the battery unit and then put it away. Do not leave battery unit plugged into the tool when you put the tool away. This will discharge and kill the battery unit.

There are non-Hitachi substitute batteries now on the market. I'm guessing the same precautions apply but I don't own one of the replacements so I don't truly know.

The actual batteries in the Hitachi BSL 1815X are Sanyo UR18650SAX lithium ion batteries. Lithium Ion cells aren't all that easy to get commercially because of handling & safety requirements. Not certain if you can take apart the 1815X and swap out the bad Sanyo cells.

Hitachi BSL1815X battery also compatible for BSL1830 battery