Energy Advice Scotland, a nationwide free information service on energy matters, says that out of 20,870 vouchers issued in Argyll and Bute for households using pre-pay electricity meters, only 15,260 were used - leaving 4,610 vouchers unclaimed.
Scotland-wide, more than 273,000 vouchers issued between October and December 2022 remain unspent.
Vouchers last 90 days, and with those issued in December expiring on March 9.
Conor Forbes, policy director with Advice Direct Scotland, said: "With energy prices still incredibly high, it’s vital that households get all the support they’re entitled to.
“We would urge any households in Scotland who have a prepayment meter to check whether you have been sent a voucher and use it before it expires.
“It’s concerning that so many people have not redeemed their vouchers and we don’t want to see a similar situation when December’s vouchers expire next month.
“If you haven’t received your vouchers, you should immediately get in touch with your energy supplier or Advice Direct Scotland’s expert advisers.
"If a voucher does expire, customers can ask for it to be reissued."
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