There's been a lot of talk on the net about the stock NiMh TDI SL battery pack. Though I haven't had mine very long I've realized pretty quickly much of what was being said was true. Mostly the complaint is that there just isn't enough "oomph" to properly power the coil which affects the depth to a degree, but more so the sensitivity. So here's how I addressed the problem on a budget and had a very noticeable improvement.
First off, here's the meter reading using NiMh batteries in the AA battery holder. These run at only 1.2V per cell. This is the same as the stock battery.
Next is the same pack filled with Alkaline batteries which start at around 1.5V per cell. It's a marked improvement, plus it will give 5 to 6 hours of use (depending on which battery) as opposed to only about 4 hours on the NiMh pack.
Now here is a pack of 8 18650 Li Ion cells (2 banks of 4 cells in parallel). These run 3.7V nominal but around 4.2V fully charged giving almost 17V out.
I was able to get the cheap holders for just over $5 a pair on ebay. The batteries I bought some time back for my flashlight but never got around to using them. There are a good off brand rated on the label at 3400mAh but in reality are only 2000-2200mAh, but still was a great price for what they are.
The pack itself with these batteries gives me around 4400mAh which should get me 5 to 6 hours run time in theory. If I upgrade to the real Panasonic high drain 3500mAh ($60 set of 8) batteries, that would give me 7000 mah and upwards of 8 hours run time.
So going beyond the math, here's how I have it put together. I found a plug set with pigtails from an old obsolete surveillance camera setup I was able to repurpose. (Free!!) Instead of having to open the control box snd wire into the power wires themselves I used the AA battery pack. I was able to simply drill a small hole, thread the wire and solder the wires to the contacts inside. Plenty of room for everything!
This leaves the plug just extending outside the box.
The battery pack I was able to repurpose an old microphone curly cable to attach to the pack and to the plug. I used shrink tubing for more insulation and to add strength to the splices.
Here's the finished pack and battery tray hooked up. As you can see the voltage is almost double the stock NiMh batteries. No problem with circuits in the TDI. According to Whites engineering it can safely handle 18V. I've heard of someone hooking 24V to it, but I wouldn't recommend it.
When using this setup the battery case just slides in as normal and I run the pigtail out the side of the battery door. The door will close and latch but will only lock on the one side without the wire. I haven't decided yet if I want to clip the battery door for clearance.
Here's the complete setup. All I have to do is slip the case into the slot in the TDI SL and pop the battery pack into the pouch on my belt. Almost too simple! I may look for a better fitting plastic hard case that fits the battery pack if I can find one.
As for performance the differences were as night to day! In the old church yard I tested it at j couldn't get any ground reading to see the ground balance using the stock battery pack. When swinging I would often get a lot of false tones as the ground would change ever so slightly because the GB was way off. Best I could do was guess and tweak as I went along.
Now add the additional voltage, I suddenly was able to get a fair tone change while doing my GB in the very neutral soil and was able to fine tune the machine before going off willy-nilly across the grass. The real signals just popped, while the irregular trashy signals were more pronounced aiding immensely in deciding to dig or not. So in my opinion a very worthwhile project!
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