Until recently I only ever used panasonic CR123A non rechargeable lithium batteries in my thermal scope.
Mine takes 4 batteries (2 in series which are in parallel with another 2 in series) so that it runs on 6 volts.
I never used rechargeable CR123 batteries because:
a. When fully charged they would have a voltage of 8.4 volts and that could well be too high for the scope
b. Rechargeable CR123s have very low capacity compared to non rechargeable batteries (650mah compared to 1400mah)
Battery life with the non rechargeable CR123a batteries is around 6 hours continuous
The scope needs more voltage to start than it does to run, so it can and does happen that the scope is operating just fine but you switch it off between shots and then it won't start up again when needed and(on more than one occasion) a shot at a fox is not possible because you're desperately changing batteries in the dark!!
What was holding me back from building an external battery pack was that the cable plug that would fit the connector on the scope is about as common as rocking horse poo.
I eventually found the same style of connectors, with right number of pins, but they were the "wrong way round" i.e the cable plug was a female and the panel connector was a male. What was needed was a male cable connector.
With some difficulty, I "modified" the connectors to create a male plug.
I had a couple of attempts at a battery pack.
The first was a plastic 2 cell battery box like this from E Bay
1pcs 2X7.4V 18650 Battery Storage Case Waterproof Battery Box w/ Switch and Wire | eBay and it finished up looking like this
This is quite neat but suffered from a major problem in that the recoil of the rifle (22-250) caused a brief loss of contact at one or more of the battery terminals resulting in scope briefly switching off.
A couple of small disc magnets on each end of each battery sorted this, but by then I had moved onto the second pack - the well known "battery torpedo" style
This uses a 2 cell torch body and tail switch, and the tail switch from a second torch. The second tail switch is disassembled and modified to take the voltage regulator and the cable comes out through the rubber push button
This time I used protected 18650 batteries (they're slightly longer) and a disc magnet at the junction of the batteries to reduce the risk of a recoil induced loss of contact.
I shot 3 foxes the other night and it worked flawlessly.
That "torpedo" stays on the scope and the 18650 batteries are removed for charging.
A set of non rechargeable batteries are also fitted in case the "torpedo" runs out of juice.
I'd expect about 9 hours continuous from the "torpedo".
Cheers
Bruce
