Have you tried getting the HR monitor and your chest wet? I had the same problem once it got colder outside and was told it can be the friction from clothes b/c the air is dry. It seems silly, but wetting everything before hand took care of the spikes. Changing the battery can't hurt if it's been awhile.

Wet the contacts
try a different shirt (static)
use hr gel

Try to wash the belt in the washing machine + wear it a bit tighter than usual

I had the same problem and switched to the polar heart strap. Issue solved

This time of year (assuming you are in the Northern Hemisphere) is definitely drier and it can take some time for sweat to build up enough to wet out the strap. Water will sometimes work, but I do find that if my skin is really dry it will just suck up that extra moisture.

I had some aloe vera gel (the kind you use if you get a sun burn) and put a spot of that on each contact and it works wonderfully. It is also much cheaper to get locally than the proper heart rate gel and you can use it later in the summer if you get a sun burn.

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Ian

You definitely need to change the battery every few months in the strap but...

The strap that comes with the 910 sucks. You may need to replace it. The older, "hard strap" that Garmin makes is excellent, only $34 at Amazon, and usually lasts for YEARS.

You replace your battery that often? I go for a year or more on mine. And I wear a heart rate monitor for everything but swimming. I did find that cheaper 2032's don't last as well as the more expensive Duracell ones.

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Ian

When I wear it for 20+ hours a week, I have to replace the battery pretty often. Whenever I'm training like I am now (sporadically), not that often. I bought a bulk pack of 2032s for Garmin Footpods, Cadence Sensors, HRMS, Powertap G3, so it's no big deal making sure I have a strong battery in there.

Thanks everyone. I ditched the original soft strap after the first couple of months and got a hard strap. Today I completely wet both electrodes and had consistent readings from the start. Will update post if problems continue.

Yep, I lick mine.

Pedal-boy, did you just get a polar strap and snap the original Garmin monitor to it? Garmin has replaced my strap twice in the past year. It works fine for a few months then gets inconsistent readings. I regularly wash it and moisten the pads. I just replaced the battery and am still getting inconsistent readings (way too high for first 10 minutes and then way too low intermittently later in the work out.

To wet the first layer shirt in that spot helps too.
Works for the latest garmin strap so far over a year now.
On the polar strap you just need to cut a little of the grommets win a blade.

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-shoki