Hi Denis,

I’ve seen this happen before. The cause is too much pressure applied to the end terminals of the battery. This causes an internal short within the battery, which makes it heat up. The internal short can happen when the meter is dropped on its end.

Your meter is probably fine if you put in new batteries and don’t tighten down too tightly. Sometimes the spring contacts are bent out of shape and exert extra pressure – please inspect them as well.

I hope this resolves the issue, let me know how it goes. Best
~James

The problem with one or both AA cells getting shorted out and overheating seems to be a design flaw in the battery spring clips. On my meter the clips have sharp inside edges that can cut through the plastic wrapper of the AA cells as they are inserted, or perhaps as the enclosure halves are screwed together or if the meter is dropped/knocked.

This causes a short circuit at the negative spring clip because the metal cylinder of the cell (under the usually thin plastic wrapper) is connected to the positive terminal.

This has just happened to me after the first battery change today. Fortunately I smelled something hot within a few minutes and realised it was coming from the meter, which I hurriedly unscrewed and took apart. One battery was so hot that the plastic wrapper had blistered and I had to yank it out with pliers. The affected battery has obvious nicks in each end of the plastic wrapper. There doesn’t seem to be any damage to the meter, fortunately.

I’ll be putting a wrap of tape around the negative end of the replacement batteries to prevent this, and trying to grind off the sharp edges. It might also work to clip off the spring arms at the negative end of each holder and rely of the plastic enclosure to hold the cells in position.

Matt,

Thank you for this write up. I tested this myself and confirmed that I could reproduce it. It seems there are two ways to make the battery short happen – with impact on the end (as I mentioned in an earlier post) and by the battery contact wearing through the battery label.

I’ll talk to the battery contact manufacturer next time we re-order and see if they have any suggestions.

Thanks
~James

PS in case it matters… my Mooshimeter is RevI 04/2015, and was purchased end of June in the UK from Elektor. The meter appeared to in standby rather than the “hibernate” or shipping mode when I got it, which might explain why I’ve had to change the batteries after only a few weeks of very light use.

Thanks for the details Matt. If the new batteries give out sooner than expected let me know, there may be something systemic happening.

~James