Not neccessarily true,.. those links mostly refer to trickle chargers and smart chargers, a battery tender is neither. Its more of a low rate "float" charger, it charges at a relatively low rate then tapers off and completely shuts off at 13.8 volts. This is completely safe for Lifepo4 batteries. "Battery Tender" is a brand name, not a type of charger. Many people call any trickle chargers battery tenders but trickle chargers don't shut off, many will taper down but not shut off completely.
Smart chargers are regular chargers with extra circuitry and often try to auto detect battery types to determine capacity and charge rates but they are designed for lead acid chemistry and are sometimes confused by Lifepo4 batteries. Some also have anti-sulfation modes that lifepo4 batteries don't like.Smart chargers also usually don't shut off completely but just switch to a trickle charge. These should be avoided. I had a long talk with the manufacturer of "Battery Tenders" and was assured they are safe.
Having said all that, you really won't need a battery tender because Lifepo4 batteries have such low discharge rates. just disconnect them for the winter and store them inside till spring. The only exception would be some newer bikes that have a small but constant draw on the electrical system. If you leave the battery connected but don't ride often, any battery will run down. These could and should use a Battery Tender or other legitimate "float" charger (not a trickle charger or smart charger)
I willl agree that there are purpose built chargers for lifepo4 batteries that can do a better job of charging but that gets confusing too. Almost all R/C type chargers that can handle lifepo4 chemistry are what is known as balance chargers. These are designed to charge through a special battery tap and not the positive and negative terminals. Thes chargers essentially act like four individual chargers, one for each cell in your pack. This also keeps the cells balanced and is a good thing except they can only be used with batteries that have the special balancing tap installed. I started out selling my batteries that way but no one seemed to care about the taps and it confused people so I eliminated them.
I haven't been able to find a simple 4 cell lifepo4 "non balancing" charger to recommend but I'm sure some will come on the market soon enough ?
You can read the FAQ's posted on the Shorai battery site to confirm evrything I'm saying.
http://www.shoraipower.com/t-faq.aspxHere's an excerpt:
Q. Can I use Lead-Acid battery chargers or charger/tenders?A.Yes. HOWEVER, you may NOT use a charger/tender if it has an automatic "desulfation mode", which cannot be turned off. We have confirmed with Deltran, makers of the "Battery Tender" brand, that their products do NOT have a desulfation mode, and are therefore OK for use with Shorai LFX, for example. But the best possible charger/tender for Shorai LFX is the SHO-BMS01, which will be released on about March 15th 2011, we expect. It uses the 5-pin BMS port in the LFX batteries, in order to monitor, diagnose, and balance the individual cells during charge. And it also has an optimized storage mode that will give the longest possible service life to your LFX.