Small sealed lead-acid battery and a (dismantled) charger used for it. Had used the battery in a plastic case with a sealed connector to power my bicycle lights for about a dozen years - wee halogen headlight at the front, and old dynamo type lamp fitted with an LED bulb replacement at the back. No bother with it over all those years, other than the fact that the battery meant carrying an extra kilo on the bike.

It was the best lighting I'd ever had, until white LEDs became available, and bright and cheap enough to use as alternatives. Switched to them and stopped using the above around 2012. Thought the battery had finally given up the ghost, which would hardly be surprising, in that I bought it last millennium! Turns out the charger was lying when it indicated it was charging the battery - the charger had failed, or I failed to check it earlier. Battery may be salvageable for a bit longer. Not sure if the charger can be. Cracking the sealed case open of such things is always a challenge, but managed to pop this one off fairly cleanly. Repair job for another day, perhaps. Trying to charge the battery with a basic variable power supply instead, which may be all I need.