My understanding is that the battery due date in the main unit is determined by
the expiration date of the Duracell batteries inside. (Presumably, the 1st day
of the month listed.) I stick a sticker with that month/year on the ELT body
and make a note in the logbook.

As for the remote unit, I'm not sure how to handle that. The replacement
battery I bought for it today (an Alkaline - couldn't find a Lithium) has no
expiration date that I can find, even though it's a Duracell brand. I'm not
sure when it was manufactured either, so I don't know how long it has to live.

I plan to make an entry in our Maintenance spread sheet to replace it in two
years. (Would have been three if Lithium.)

Nor am I sure about requirements for a logbook entry for it and a sticker for
it. (IIRC, ACK didn't supply any for the remote when we bought our unit.) It
might be that the remote is considered part of the "ELT" as a system, and
requires the same documentation as the ELT proper. OTOH, since there's no
expiration date (that I can find) for the remote battery, maybe the remote is
an area conveniently overlooked by the regulators as being "distinct" from the
ELT. (The ELT will still work without a battery in the remote.) I suppose the
most prudent way to proceed is to make a sticker and a log book entry and a
guess on the replacement date.

As for practical replacement of the main batteries - yes, I was alerted by
another ACK user that the batteries in his unit leaked, even though well short
of the expiration date. I checked ours, and found the same. (Duracells.) I
cleaned everything out, and now make it a point to physically remove the
batteries at ever annual and also replace them prophylacticly 50% to their
expiration date.

This isn't the first time I've had Duracells leak - happened in a MAG
flashlight too. I live in hot Phoenix, so if not a design flaw, perhaps our
heat has something to do with it. (User that had his leak lived in higher
(cooler) country in Arizona.)

Have you ever had problems with battery leakage in an ACK ELT. I have heard
of number of cases.

Hope this helps,

Mike Palmer
Excellence in Ergonomics