I was asked to repair a lantern with a sealed lead acid battery. It was not properly maintained and sat uncharged for a couple of years. It would not charge, so I opened it and found it to be bone dry. I refilled it, but it is obviously a victim of sulfation as it has virtually no capacity.

Clearly, I need to replace the original battery (SEL DMU 6-3) to salvage the lantern. Extensive searching proved an exact replacement is not available. The closest I've found is a Tempest TR2-6 (almost the same dimensions, but 2.3 AH vs. 3 AH). To compensate for the lower battery capacity, I was considering replacing the original 6V 3W Krypton bulb with a 40 lumen LED bulb (e.g., Dorcy 41-1664).

So, my questions are:

* Does replacing the Krypton bulb with an LED bulb sound feasible?

* The original charger appears to be a simple AC adapter (6V 100mA). Charging Lead Acid discusses the importance of 3-stage battery charging. Tempest does make a corresponding 3-stage charger for the TR2-6. Would it be a wise investment to purchase a 3-stage charger, rather than continue to use the original charger?

 

If the flashlight will be used infrequently, you don't need the 3 phase charging algorithm. You have plenty of time to recharge it before the next use. As you have found out, not charging (letting self-discharge happen) is not an option.

I find that I can keep SLA (nearly) fully-charged by floating it at 2.28V/cell (at 25degC). The "charger" must be well voltage-regulated (6.85+-0.05V), and intrinsically current limited by the wall-wart transformer, so if you happen to hook it to a dead battery, the current will not overheat the transformer, regulator, or battery...

You build such a charger by starting with an unregulated wall-wart, and putting a Low-Dropout regulator IC between the wall-wart and the battery. Dont overlook the easy way (the PB137). Wouldn't it be cool if they made one for three cells instead of six.

In keeping with my sig line, when charging a battery, current flows into the positive pole of the battery

 

You can take one step at a time.

1) Replace the SLAB with the 2AH battery.
2) Try charging with the 100mA charger and see if that works.
3) The Dorcy 41-1664 lamp you quoted is a 2.25V 0.6A Krypton bulb. You can try to find a high intensity LED replacement that takes a lower current.

 

Many thanks for the advice. I'll use the original charger and see how it goes.

BTW, my original post had a typo - the LED bulb is a Dorcy 41-1644.

 

What is the current draw of the Dorcy 41-1644 LED?

 

Dorcy does not provide any power or current draw info for the bulb. I have seen some info in customer reviews. They indicate krypton bulbs draw 700-800 mA (which my measurements confirm). The Dorcy is reported to draw around 100 mA.