Martin said: > Does rercharging make them heavier... Yes - charging adds about 20 nanograms of electrons per milliamp-hour. See below. E&OE / YMMV. Electron mass to charge = - *e* / *m**e* = -1.758 820 ... E11 C/kg 150(44) [image: \times 10^{11} {C / kg}]. 1 Coulomb = 1 A.s A 2000 mAh cell will gain 2000 mAh / 1000 mA/A * 3600s/h ~~~= 7200 Coulomb when charged. This will mass 7200 / 1.76E11 kg or about 4E-8 kg or about 40 micrograms of electrons. Or, about 20 nanograms per mAh. Russell McMahon 2009/11/3 Martin Ryder > Hi Russell, > > Thanks - backs up my suspicions! > > Does rercharging make them heavier... > > Martin R > > > --- On Tue, 3/11/09, Russell McMahon wrote: > > > From: Russell McMahon > > Subject: Re: [EE] Advice on batteries for consumer use > > To: "Microcontroller discussion list - Public." > > Received: Tuesday, 3 November, 2009, 12:56 AM > > > > When considering 9V , AA > > and AAA batteries .... does one get the best > > > > bang for the buck with ....... > > > > primary alkaline > > > > primary NiMh > > > > secondary NiMh > > > > YMMV. > > E&OE. > > > > AA has about 2+ x AAA capacity and are often of similar > > price. > > AAA are generally an abomination unless small size is an > > essential. > > AA with boost converter will usually give better energy/$ > > and energy > > volumetric density than AAA. > > > > Alkaline AA have ratings hardly more than the latest top > > NimH. > > Generally under 3000 mAh in each case, so far. > > NimH have a better sustained high current capability. > > Various magic technologies may give primary Aa cells more > > current > > sustainability but the mAh seems little affected across > > Alkalines and > > consumer "Lithium" cells. > > > > This is a retail reseller page but gives a good idea of > > available > > primary Alkaline mAh capacity at different sizes from one > > maker > > (Eveready). > > > > http://www.batterycountry.com/ShopSite/alkaline-batteries.html > > > > Eveready have far far more data available but it's not > > usually all in one place. > > > > When it comes to serious AA use, buying NimH is the > > overwhelmingly > > most cost effective choice wrt Alkalines. > > NimH cycle life is often said to be 500 cycles but DO read > > spec sheets > > to see the conditions. > > Under deep cycle use "rather less" may be achieved. > > Under light depth of discharge rather more. > > > > LiIon cells are nominally 3.6V. > > They CAN be had in AA / 14500 form factor. > > Some people use these with a spacer to give the voltage of > > 2+ x Alkalines. > > Alkaline Voc new is 1.55V. > > LiIon needs special chargers. > > Using them bare in place of AA's is living dangerously. ALL > > LiIon > > should have inbuilt protection circuitry but some AA do not > > for > > certain. Even some 18650 do not but that is less common. > > "Vent with flame" is a significant risk with unprotected > > LiIon. > > And a risk with protected LiIon. > > > > The new great hope is LiFePO4 / Lithium Ferro Phosphate. > > About 3.2V means terminal voltage. > > Volumetric energy densities maybe somewhat above NimH. > > Cost should be 2 +/- 0.5 x NimH price but actually vary > > quite widely. > > 4 x 400 mAh LiFePO4 could be had at Walmart for $US10 a > > while ago. > > Claimped AA LFP capacity is often 600 mAh but probably more > > like 500 > > mAh and can be lower. > > Anything out of China of no-name type can be MUCH lower at > > any stage. > > LiFePO4 can be superb and terrible depending on maker. > > 18650 LiFePO4 cell is about 1100-1200 mAh typical and maybe > > a bit more > > but not much. Anything marked eg 1400 mAh is suspect for > > capacity so > > probably for other things as well. > > Special charger needed. Similar to LiIon but with > > differences. > > > > > > I have seen AA LION batteries advertised. How > > is this possible? I > > > > thought LION was 3.6V. > > > > As above. > > Yes, it is. So ? :-) > > ie don't use on 1:1 basis. DON'T charge in std charger. > > > > > If one wants to keep all the battery powered toys > > going , what is the > > > best choice now ? > > > > AA NimH usually. Reputable brand. > > As others noted - SOME devices need Alkaline voltage levels > > and NimH > > may be too low. > > > > Some people are using LiFePO4 AA + 1 spacer to replace 2 x > > Alkaline AA. > > Max voltage may be a bot high but most products don't > > care. > > LiFePO4 will discharge to 2V safely typically although > > higher is kinder. > > Lower is not recommended. Cells should have internal > > protectors BUT > > far less dangerous than LiIon. > > > > > Are cheap batteries from China going to be a safety > > issue ? > > > > Most batteries come from China. > > Cheap ones MAY be good. Or not. > > Bad Alkalines are usually just low performance. > > Bad NimH will usually not burn etc too too often or much. > > Bad LiIon may be fun, depending on what they are in when > > they go bad. > > > > NimH goodness can be sort of checked [tm] by weighing or, > > lacking > > scales, by "hefting" in hand. Similar specs from different > > suppliers > > should weigh similarly. Low weight is usually an indication > > of junk. > > Alkalines also should weigh similarly to each other. > > > > NiCd weigh somewhat heavier per mAh than NimH. A 'nice and > > heavy' for > > the size but low capacity NimH may really be a NiCd. > > > > For toys self discharge / shelf life doesn't usually matter > > much. NimH > > rate is highish but has been getting better for some > > years. > > If it does matter then newer low-self-discharge NimH are > > available. > > Firstish was Eneloop but now there are many brands. The > > actual > > technological cost of doing this is low (mainly a thin > > coating of > > Copper on Ni powder during manufacture AFAIK but I may well > > be wrong) > > - I'd expect this to become the NimH norm in a few years. > > > > IF you have tight control of battery replacement and > > charging then > > LiFePO4 is liable top give the cheapest per cycle cost > > battery over a > > long period. I'm about to do some serious playing with them > > ... :-). > > > > > > Russell McMahon > > > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist