NiMH batteries

    On March 5th, 2010 Vincent G. wrote: I have a problem, let me explain you... I am actively looking to buy a replacement battery for my Roomba Vacuum and I know it is possible to buy a NiMh battery.  While looking at the different battery quality between NiMh manufacturers, some sellers have claimed that component quality between manufacturer ends up in better NiMh batteries.
    What should I know that helps me to select a manufacturer when times come to buy a new NiMh batteries?
    A seller also claimed that China and South Korea should be avoided and that Japan makes better NiMh batteries.  I am aware that he's selling Japanese cells battery so he was not really objective.  When I asked him to support his claims, he couldn't give me any source that proves it.
    What makes a good NiMh battery? Thank you in advance!

        Sincerely,
          Vincent G.


     Doctor Atomo to Vincent;
    When I talked to a manufacturer, they said the more nickel they use a NiMH battery the higher capacity and longer lasting they are.  The more nickel in a battery the heavier the battery is.  If you have them in hand generally the heavier they are the better.  This is not something you know by looking at an ad however...
    I wouldn't say that batteries from China or Korea are bad.  I know that China makes some of the highest quality products and some of the crummiest.  It depends upon what the reseller decides to purchase.  It is true that consistently, the highest rated batteries are made by Sanyo, a Japanese company.  However they are also very expensive.
   Usually the end user judges the quality of a battery by its milliamp-hour capacity, but, importantly, not all batteries actually have the advertised capacity, this is where you can get in trouble.
    I have found Tenergy brand batteries to be the best price to quality ratio. I use a La-Crosse battery charger;

    http://www.lacrossetechnology.com/900/index.php

which charges the batteries, then discharges them and measures the actual capacity of the battery in Milli-amp hours. It only does AA and AAA batteries, it costs around $75. There are other more expensive chargers that test C and D and 1/2 D etc.
    Have you found this site?;

    http://www.robotreviews.com/chat/viewtopic.php?t=231

    Good luck!, Please let me know what you do!

          Doctor Atomo


     Vincent G. wrote back;
    After you answered me, I did a comparison of every Roomba Battery on the market for series 500 (those at 3300mAh).  I contacted all sellers, and compiled their data. My XLS file is interesting to see differences in weight between them.  I also did a test comparing the weight of the cheapest 2700mAh NiMH battery on available on eBay and the highest quality 2700 NiMH battery available on eBay manufactured by Sanyo.  The results confirmed your hypothesis of the weight versus quality... { ...the cheapest NiMh battery weight was 18,5g and the best quality NiMh from sanyo was 27g.}
    While doing my searches, I discovered a 3500mAh battery, (200mAh above the highest quoted on the web) and tried to contact the manufacturer to see if I could order from him, but I was left without answer... after all that done, I was occupied by some other projects, but I eventually expected to continue later trying to find the best replacement battery available for my Roomba 560.
    About your link, at first I thought it was about building replacement batteries for series 400, but I did clicked it today, and realized it was possibly for series 500 also. I will look through this later. Thank you for your precious help, Vincent