It looks like the hunt is back on, for a good 8-cell rechargeable "9V" battery.
As my friends and I started to use Digitrax wireless DCC, we quickly found that we needed to find a source for cheap 9V batteries that would last at least for one operating session. Even some of the higher priced "brand name" batteries simply couldn't last for an entire session. Rod and I originally opted for Aldi 9V batteries which cost about $2.50 each, and could last for nearly two sessions if we were lucky.
I did some testing on my DT402D throttle and found that once the output voltage from a 9V battery dropped below about 7.5V the battery could not be used. In fact, once the voltage fell below 8 volts the throttle could perform unreliably.
In the interests of economy and reliability, I started looking into buying some rechargeable batteries. From various internet forums, I knew that many Americans favoured a particular high-end brand of battery that cost somewhere in the order of AUD $15 to $20 (to which I'd have to add S&H costs.) I also found many comments that some well known brands of rechargeable battery were not suitable as they did not hold enough charge.
On doing some research I found that "Rechargeable nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) batteries have between six and eight 1.2 volt cells." Doing the arithmetic:
6 cells @ 1.2V = 7.2V
7 cells @ 1.2V = 8.4V
8 cells @ 1.2V = 9.6V
Obviously, not all 9V batteries are created equal. In fact, many (most?) don't even hold 9 volts when fully charged. The hunt was on to find some 8-cell batteries at a good price.
While I was searching, I discovered that on eBay it was possible to buy rechargeable 9V batteries for under AUD $4.00 each, including S&H to Australia. At that price I thought "what have I got to lose?". Even if they lasted for only two or three sessions before I threw them away, I was in front (compared to the cost of the Aldi batteries). So I got my order in, and bought a pair of batteries that look like this:
After buying my first lot, I bought a second pair (for about the same price), which look like the one in the next photo, except that where these say "POWER", mine say "FEEBY":
These batteries are slightly smaller than the BTY batteries, and will fit in the DT402D and UT4D without trimming off the tabs. In all other respects though, my FEEBY batteries seem to be just as good as the BTY batteries.
It has been more than two years since I bought my batteries, so I can't say with certainty that the batteries now available on eBay are still good value. So if you do get some, please share your experiences on what you bought and how they perform by posting a comment here.