On YouTube I found the following, fairly useful guide:
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The battery offered here (D = 17mm / L = 48mm / 2700mAh) has the same diameter as the old / original battery (D = 17mm / L = 42mm / 2150mAh / HR 4 / 5AU), only it is a bit longer. In my opinion, this is due to the higher capacity. The battery but still fits in the casing (see uploaded photos). The spring between the motor and battery is compressed a little more, thus the installation of spring is something fummeliger. For the solder tail from the positive terminal does not need to be angled grand as the old battery, but can almost just be pushed through the printed circuit board. The only adjustment that you have to do a leg is cut from each of the respective solder tail (cut or good pair of scissors) before the battery mounted on the PCB and then soldered.
The battery exchange is now back 1 month and I'm back fully satisfied with my old / new toothbrush. I invite the brush once fully and use them always, until it is empty without having it continually stand in the charging station (longer battery life). When the battery pack once again faded away and the toothbrush is technically still OK, I'm going to order me there again this battery.
In other reviews often about the price and the original battery (HR-4 / 5AU) is discussed. Clear one gets the "HR-4 / 5AU" online between 5-6 euros, but since after all, still 4-6 Euro Vesandgebühren happen. Thus, the battery offered here is a good deal with about 12 Euro and higher capacity.
I hope I could help you in deciding.
MfG
