300V in a battery

One of the exposure meters in my collection (a Radcal/MDH 1515) uses this Eveready #493 300V battery as bias voltage source for the ionization chamber used to measure x-ray exposure. The rest of the meter is powered by 4x2V rechargable lead acid batteries in a D cell form factor.

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Looks like this battery was installed in December 2002. Last calibration date for the meter was 2003, so it was probably replaced when it was sent in for the previous calibration.

After 16 years of sitting on the shelf, the battery is pretty flat.

Let’s take the cardboard off and have a look at what’s inside.

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There are 10 plastic wrapped packs, each 1.3 cm x 2.2 cm x 6.6 cm long, all connected in series. Each pack appears to have 20 individual cells coated in a waxy type material and wrapped in plastic to hold them all together. With 200 cells, that gives 1.5 V for each cell.

Looks like there’s been a bit of leakage while the battery sat on the shelf for the past 16 years.

A close up of one of the packs.

Neat stuff.