AA batt question

[KI4HNN]

Hi all,
I have a Yaesu FT60 handheld.  I bought the AA battery case to go with the radio.  I have been using 6 AA duracell rechageable NIMH batterys rated at 1800mah.  I have noticed that when I go to transmit on high with the radio the voltage drops down to where the batt indicator comes on.  I can still hold a conversation ok.  This leads me to several questions.  1. I wonder are the batterys getting fully charged each time they are recharged?  2. Would nicads be better since they can handle larger amp loads?  I am only pulling 1.5amps max on the nimhs, why would the voltage drop over a volt each time the radio is keyed? ex: radio is reading 7.5v keyed the voltage drops to 5.5v?  
Any suggestions. When not doing a lot of tx on the radio the batts last a long time.

Help,
Joey
KI4HNN

[KE4SKY]

NiCd and NiMh batteries are typically 1.33-1.4 volts when fully charged and 1.2 volts when fully discharged, whereas AA alkaline cells are 1.6-1.7 volts when fresh at full charge and 1.5 volts when discharged.

While the amp-hour capacity of your rechargeables is adequate, their lower voltage makes the radio think it is trying to pull current from discharged alkalines, which is why it is powering down.

Not all AA alkalines are alike either.  An article in Practical Sailor several years ago compared performance of AAs of several brands in various devices.  Duracells hold up better in cyclic use requiring surge capacity such as in handheld VHF transceivers and photo flashes.  Everready gives longer burn time in continuous low-current applications such as LED flashlights.    

[KI4HNN]

Thanks for replying. What you said makes sence, but there is something that I don't understand.  The battery pack that comes with the radio FNB83 has nimh cells in it, if using nimh cells in the battery holder makes me think that the radio would act the same either way?  Exactly what is in the FNB83 that doesn't cause the radio to do act like that?  If someone please shed some light on this because it has puzzled me for a while now and I can't seem to figure it out.

Thanks,
Joey

[AD5X]

On high power, the FT-60 can draw 1.5 amps at 5-watts out.  The problem with these AA holders is that they use spring contacts and steel wires, resulting in more resistance (and therefore more voltage drop) than you would see in the normal welded-termninal battery packs.  I measured the voltage drop in a typical AA holder at 0.1 volts per interconnect pair at 1.6 amps (see www.ad5x.com). So this says you could have maybe another 0.5-0.6 volts drop due to the battery holder.  And then couple this with the lower cell voltage of NiMH or NiCad cells.

Phil - AD5X