First, the word itself. In Japanese, 'battery' is rendered as 電池 denchi, lit. 'electricity reservoir'. The second kanji also translates 'pond' and (small) 'lake', Japanese ike.
Second, where the word turns up. Denchi first lodged permanently in my mind while I was doing fieldwork in Yap, Micronesia, where (1) I was dependent on batteries for my flashlight and portable cassette-radio while living out in a village without electricity (at that time, anyway); and (2) people had managed to borrow a lot of Japanese vocabulary during three decades of Japanese rule (1914–1945), like sikoki 'airplane', and sikojo 'airport'. Some of the more amusing borrowings are now archaic, if not obsolete, in Japanese, like sarumata 'traditional Japanese men's underwear' (now used with reference to adult diapers) (Yapese didn't need to borrow a word like fundoshi 'loincloth'), chichibando 'breast band' (definitely a foreign concept in traditional Yap), and kachido 'movie' (< Japanese 活動大写真 katsudou daishashin 'moving big picture').
Third, how the items so labelled are subclassified. The relative sizes of the old familiar cylindrical dry-cell batteries are indicated numerically in Japanese, ranging from largest to smallest: 単１形 tan-ichi-gata (D cell), 単２形 tan-ni-gata (C cell), 単３形 tan-san-gata (AA cell), 単４形 tan-yon-gata (AAA cell). My electronic dictionary requires two 単４形, my digital camera requires two 単３形 (I forgot to bring my recharger), and our gas stove requires two 単１形. I've recently had to replace all three sets. At least I don't have to carry two spares of the largest size around with me. (BTW, Philbert Ono's Photowords is a great resource for translating photography-related vocabulary, including battery types, between English and Japanese.)
Finally, when I removed the Fujitsu 単１形 batteries from the stove and looked for the size designation, I first thought they were 単０形. After all, the midnight hour in Japanese is 0:00 reiji 'zero o'clock'. But the characters surrounding the 0 were making a different claim: 水銀０使用 suigin zero shiyou 'mercury zero use'. When I examined the other replacement batteries I had bought, they all made the same claim, no matter whether the brand was Maxell or Fujitsu (both made in Japan), or Konnoc (made in China). I hadn't kept up on dry-cell battery technology. Fujitsu Magazine (July 1997) explains.
By using purified materials，a special zinc alloy powder，and a zinc-indium-bismuth-aluminum anode，and by establishing clean production lines，we have been able to develop an alkaline-manganese dry battery that has no mercury．The discharge rate of the battery was improved by remodeling the structure of the cathode．Moreover，by remodeling the anode disc，the battery has been made much safer．There are still a few other products from which mercury needs to be eliminated.
Also，since 1996 we have been producing ferrite cores for the deflection yokes of cathode ray tubes using raw material recovered from spent dry batteries.
POSTSCRIPT: It's good that Japan is trying to restrict mercury pollution, which caused Minamata disease. BTW, the Japanese (and general Sinitic) compound for the element mercury 水銀 suigin translates literally as 'water silver' rather than 'quick (i.e., living) silver'. The planet Mercury is 水星 suisei 'water-star', and Wednesday is 水曜日 suiyoubi 'water weekday', which matches pretty well the Romance-language names for the same day of the week: Romanian miercuri, Spanish miércoles, Portuguese mercoles, French mercredi.
UPDATE: Reader Peter North adds a comment and query:
Sorry, I can't resist reporting a new usage in Philippine English, not "Taglish" (since 2003). "Low Bat" describing a child lacking energy - needing food or sleep. Presumably derived from abbreviations on cell phone displays - you appreciate how widespread and central to life cell phones have become. Anyone seen this elsewhere?