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TDI Pro - External Battery Pack
Posted by: sandbandit
Date: July 15, 2017 01:15PM
Got creative recently and made an external battery pack for my TDI Pro - mostly because the stock battery was no longer available when I purchased my machine (no spare battery), and the stock battery it came with doesn't last very long in the field (about 4 hours of good power). The stock battery is 14.4 volts / 4.8 amp hours.

The new battery pack consists of 12 rechargeable "C-cell" NiMH batteries, wired in series (1.2 volts each x 12 batteries = 14.4 volts) held together using two 6 "C-cell" battery holders wired together "+" to "-". Fresh off the charger the voltage measured a safe 15.69 volts (less that the 18.5 volt maximum for the TDI Pro). Each battery is rated at 5000 mAh (5 amp hours = 1 amp draw for 5 hours), and when all 12 are connected in series it has 60,000 mAh (60 amp hours = 1 amp draw for 60 hours).

The TDI Pro draws 0.6 amp, so from a full charge to zero power = 100 hours (60 divided by 0.6). Naturally, battery capacity ratings are typically overstated so actual performance is less.

The bottom line is that this battery has a LOT of stored power, and I can to hunt for several days without having to worry about a low battery. No need to carry a spare battery either. Recharging is pretty fast - I recharge all 12 batteries at once in 3 EBL chargers - it takes about 3 hours.

The new external plug-in does not defeat the original design, so you can still use the stock battery inside the box by itself if you want. The cost to assemble everything was reasonable (12 batteries, 3 chargers, 1 pouch, 1 web belt, 2 battery holders, and assorted wiring) worked out to be less than the price of a new stock battery.

Pros: Long battery life (14.4 volts / 60 amp hours)
Lighter metal detector (stock battery removed)
Fast recharge time

Cons: Batteries must be removed from holder for re-charging
Battery pack is carried on your waist with a web belt

San Diego

Re: TDI Pro - External Battery Pack
Posted by: TN Mike
Date: July 18, 2017 11:48PM
I'd love to have a TDI. If I get one I'll be back here to follow this mod, Thanks!

Re: TDI Pro - External Battery Pack
Posted by: sandbandit
Date: July 24, 2017 10:41AM

The 1 x 12 "C" NiMH external battery pack produces 5,000 mAh (similar to a single stock battery in power - but pretty heavy at 2.2 pounds)
The 1 x 12 "D" NiMH external battery pack produces 10,000 mAh (similar to 2 stock batteries in power - but much heavier at 4.5 pounds)

My apologies to the Forum members for my posting of inaccurate power ratings for the 1 x 12 batteries. AJ was correct in pointing out this mistake, and recommending the use of 26650 (or similar) Lithium Ion batteries which have a much better power-to-weight ratio. For example: a 1 x 4 Lithium Ion 26650 battery pack (16.8 volt / 5,000 mAh) would weigh about 13.85 ounces (less than 1 pound), and a 2 x 4 Lithium Ion 26650 battery pack (16.8 volt / 10,000 mAh) would weigh about 27.71 ounces (less than 1 3/4 pounds). Much better power-to-weight than NiMH batteries.

Thank you AJ for your recommendation!

San Diego

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