Sounds to me like both batteries have at least one cell below 3.0V...essentially a "dead"battery...which all chargers I'm aware of will 'refuse' to charge. Thankfully, there's is a simple, easy, and relatively safe (as long as you keep an eye on things) way to "resurrect" the packs. Of you check YouTube, you should find at least a few videos showing you how to do it. One of the (possibly THE) best was done by RC Review. Thanks to some input from a few others, I figured out how to do it even before that video was published. For all but the final step, you can do one pack at a time, or both packs simultaneously (on "dual", or higher, chargers). Here's the 'short version':
1) First, plug ONLY the pack's charging lead (ie. the connector that also plugs into the ESC) into the charger, but do NOT plug in the balance connector.
2) Set the charger to 'NiMH'...do NOT set it to charge 'LiPo' (this will be explained, below)...and set the pack capacity to be charged.
3) Set the charging Amperage to the charger's lowest possible setting, and start charging the pack.
4) This is where you REALLY need to keep an eye on the charging, and check individual cell voltage approximately every 3-5 minutes. The goal is NOT to fully charge the battery...you only want to get ALL cells above 3.0V...but, not too much higher. Since the balance plug isn't being used, that's another reason to keep an eye on the battery.
5) Every few minutes (I suggest 3-5), stop the charging, and check the pack's individual cell voltage. This can be done by plugging the balance connector into the charger (just remember to unplug it again before continuing to charge as 'NiMH'), or by using a separate "battery checker" (the method preferred by most). Once ALL cells are above 3.0V (and, hopefully, not any higher than...say...3.4V), you can skip ahead to step 7.
6) If any individual cells are still below 3.0V, repeat stairs 1-5, and keep repeating them until ALL cells are above 3.0V.
7) Once ALL cells are above 3.0V, reconnect the pack to the charger, including plugging in the balance connector, and continue charging in the normal way (ie. as 'LiPo').
The reason for setting the charger to 'NiMH' (step 2), as well as not plugging in the balance connector (step 1) is because NiMH packs don't have balance connectors, and you're tricking the charger into "believing" its charging NiMH packs. Thing is, NiMH packs don't really have a "minimum voltage", this the reason chargers can be 'tricked' into charging a LiPo as if it were a NiMH. At the same time, since the battery chemistry is different, there are two reasons why you NEED to keep an eye on it - one (obviously) is so that you don't charge the voltage to both, the other is to keep an eye on the battery's temperature (you don't want it to overheat...talk about a potential fire hazard).
As long as you never let LiPos get below 3.0V/cell, you shouldn't ever run into this problem again. That's why it's important to always utilize an ESC's LVC and/or add a "low voltage sensor" to your vehicle/vessel. Two final things to remember:
A) After using any LiPos, is you know of will be at least a few days before you'll use want particular pack again, charge/discharge it/them to 'storage' level. Almost all chargers (except Traxxas) have this ability.
B) In regards to packs previously put into 'storage', if any packs are not used within 2-3 months, check their voltage (total, as well as individual cells...best accomplished with the aforementioned "battery checker"). In your 'periodic' checking, if any packs have cells below 3.4V, recharge that/those pack(s) back up to 'storage' level. Most chargers use 3.8V/cell as the "standard" for 'storage mode'. If your charger has a user-programmable setting, program it for no lower than 3.75V, and no higher than 3.85V (I have mine set for 3.79V/cell).
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