Those of you with a Spektrum DX6i transmitter will know that the LCD display constantly gives you a battery voltage reading, and that under 4.8 volts the transmitter will warn you about low voltage. What is annoying about this system is that while it's great to show you the voltage, battery consumption differs wildly between Alkaline and rechargeable batteries.
For example, you might feel great that your Alkaline batteries are reading 6 volts, but you can be surprised by how quickly the voltage drops as the battery discharges. In comparison, if you use rechargable Nickel-metal Hydride batteries, the charged voltage can often be less but the voltage reading doesn't necessarily change as greatly as the battery discharges. The DX6i voltage meter has to basically "split the difference" because it has no idea what kind of batteries you are using. And because of this, it errs on the side of caution.
My Spektrum DX6i came with a set of Nickel Metal Hydride (NiMH) batteries rated at 1.5 amp hours (1500mAh), and they were pretty crap with regards to holding a charge. Straight off the charger after a good three cycles of charge and discharge, they only ever show about 5.5 volts, which on the DX6i voltage display looks very close to the "too low" mark. And this can make you concerned. Certainly it makes *me* concerned, even when I may not need to be.
Enter the Low Self-Discharge NiMH battery. I went out today to pick up a set of rechargables and was about to grab a set of 2500mAh AA batteries when I saw a pack of what was called "pre-charged" NiMH batteries, of only 2100mAh capacity. I was curious - a pre-charged NiMH battery? How can that be - they're supposed to self-discharge when on the shelf! I ended up buying this pack, but shortly afterwards felt bad because maybe the extra 400mAh of the standard pack would come in handy.
When I checked Wikipedia (link above) for the details on these batteries though, I was surprised to read they are indeed a new type of battery, released onto the market in 2005. And have a look at the features which I ripped from Wikipedia:
- Voltage is more stable (less load- and capacity-dependent).
- Reduced heat buildup when the battery is quickly charged or discharged
- Higher efficiency
I discharged this battery pack today (4 AA batteries) down to 4.2 volts, and then charged it back up between .8 and 1.1 amps on my Thunder T6 charger in Delta-peak mode. When it finished, the pack read a comfortable 6.0 volts on the DX6i, which is very nice and quite similar to a fresh pack of Alkaline batteries.
If you wear an anorak, you might tell me at this point that I'm actually less safe because these new batteries have more of a voltage "cliff" where the voltage will not drop much until the batteries come close to being flat, before dropping suddenly. Well NUTS to you, sir: the voltage warning of the DX6i is 4.8 volts, which will give me plenty of time to land my plane, thanks.
All up, I thoroughly recommend these new low-self discharge NiMH batteries for your DX6i, DX5e or DX7. They are for sale nearly everywhere, and you can pick 'em by their "pre-charged" or "ready to use" branding and maximum capacity of about 2100mAh.
As always, cycle your batteries a few times (discharge and full charge) and be aware that some cells can be duds from the factory!