Does anybody with any info re ID pin on dewalt 18/20V power tool batteries ?

Thread Starter


Joined Feb 8, 2018
Hello Everyone,
NeeBee here. Anybody with any info re ID pin on dewalt 18/20V power tool batteries ?
I am trying to run a DeWalt drill with Makita battery, crossed over +/- but there two more terminals TH and ID on the drill side. TH is the thermistor but have no clue of ID pin.
Any thoughts from seniors in the forum ?

Mods Note:
Please don't hijack other member's thread.
This thread was split from -- Power tool battery (li-ion) specs/wiring/etc.

Dean Rantala

Joined Sep 27, 2018
Yes, I am gonna be THAT PERSON to bring a dead thread back from the grave but...

For the search engines and others who may be looking for this info - as well as a FIX to a very common battery issue..

1) The ID pin is nothing more than a resistor between the BAT(-) pin and the ID pin.

I noticed on my smaller packs, this seems to be around 1k ohm. On my 5ah packs, this shows as 800 ohms.

2) Fix for a common issue: pack still has 1 or 2 bars, but will not charge.

You may experience this - even still works in some (maybe not all) of your tools. Pop the battery on the charger and the charge indicator light may just give one quick blink and nothing. Some chargers do not even give a single blink. As if there is no battery on the charger (battery not recognized).

I have had this issue TWICE now (both times w/ generic packs) and upon opening the pack to look for dead cells... all checked out fine. But I discovered: the resistance between GND (Batt -) and the ID pin was OPEN.

I found that the on-board 800 ohm resistor on these cheap knock-off batteries seems to fail at very high rates. Soldering a new 800 (or even 820) ohm resistor between the ID pin connection and the BAT(-) from the backside restores full battery functionality and all my DeWalt chargers recognize it once again and it operates as it should.

I own several of the Waitley 5ah batteries and not only have I personally had this issue, but Amazon reviews seems to reflect this same issue with countless others.

I suspect when the charger (or perhaps tool) passes a small current through this in order to "detect" the battery, it sends just a tad too much for the tiny under-rated resistor these generic packs use and it fries the resistor.

Further info regarding DeWalt battery charging logic

If you probe the corresponding ID pin on the battery charger side, you will find that it outputs a small voltage. It seems that the charger (and tool) are designed to "detect" what battery is installed (more specifically, the cell arrangement) by detecting the resistance.

I have a rather larger collection of DeWalt batteries ranging from the 1.5ah to 9ah (flexvolt) and have found that the resistance between ID and BAT(-) directly correlates to the number of battery parallel connections within.

5S1P == 1K Ohm
5S2P == 800 Ohm
5S3P == 600 Ohm

Following this pattern, I would venture to say that a 5S4P battery (which I think the 15ah packs are) would likely read out 400ohm. However - I do not (yet) have any 12ah packs, so am unable to verify.

This tells the charger how aggresive it can charge the pack overall. This is especially important with fast chargers. The more series cells you have doubled up (in parallel), the more current you can push to the pack.

I also imagine this also lets the tools (that need to know due to high-current use) know how much current they can pull from the battery. Obviously, a pack that reads 1K is not going to be able to provide as much current as a pack that reads 800ohm.

The TH pin (thermal) is nothing more than a thermistor between the battery (+) pin and that TH pin. It should measure between 10k and 12k at normal temp. Very simple.


While the DeWalt batteries to not really have a BMS, they DO seem to have a basic charge-balancing circuit. There is no over/under cut-out circuitry. The C1/C2/C3/C4 pins are directly wired between each cell pair and the corresponding pin via rather thin wires (regardless of the pack brand) which tells me these wires are more for "providing" the exact voltage level to the charger so the charger knows to stop the charge if one of the cell groups gets too far out-of-balance from the rest (bad cell, balance circuit cannot compensate). Other than the balancing circuit, the DeWalt 20V (or 18V for those on the other side of the Atlantic) battery is mostly just a "dumb pack". The charge protection is in the DeWalt chargers and the under-drain cut-out protection is in each tool.

Makes sense honestly. I rather pay a slighly higher price for the tool once and be able to load up on cheaper batteries -vs- a tool that may still be pricey but each battery is ALSO higher.

This also explains why the price of a DeWalt battery overall is almost the same price as buying the bare cells - and in some cases (when on sale online) can literally be CHEAPER.

Hope this helps someone.

For the search bots: DeWalt battery pinout, DeWalt battery repair, DeWalt or Waitley battery not recognized