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I had a blood pressure monitor that always read about 20 points less than the doctor's monitor. After some time, I called the manufacturer to ask about it. They replaced it with a new monitor. It also read some twenty points less than the doctor's monitor.
Note that I never had to change batteries in the first one. So, I do not know what batteries were in it. With the new monitor the batteries began to die after only a few months. I opened it to change batteries. It had Kendal AA alkaline batteries in it. These batteries were slightly smaller in circumference than my usual Duracell. The Duracells did fit and I put them in. They not only work fine but the reading now matches the doctor's reading. I find that most interesting.
Question (1) Is it safe to change from the smaller Kendall to the larger (not much) Duracell? Note that neither is a rechargeable battery. At least neither says it is.
Question (2) Could the earlier misreadings have been due to the smaller batteries?
Yes, and yes. More accurately, the discharge of the battery while powering the air pump may lower the voltage. If the circuitry design is simple, it could give an erroneous reading. When my monitor has batteries that are beginning to age, it does the opposite and reads a falsely higher pressure.
The usual applies, cuff needs to be tight, you want to be sitting with cuff about arm height, not have eaten within the past half-hour, etc.
ALSO... the automated monitors in hospitals and offices are NOT as accurate as a doctor taking your pressure manually... AND... if you are 65 or older, BPs of up to 150 are common and not a reason for panic. Lowering it is prophylactic and highly recommended, but a BP up to that is not automatically a sign of a major problem (although it is POSSIBLE that it is an indicator) AND... some people have "white coat syndrome" where the BP spikes in a waiting room from the anxiety of the visit. A lower reading at home could be indicative of that. The simple thing to do to check for that is to bring your home monitor in, and have it compared to the reading the doctor gets at the same time.
Thank you, Harry. These batteries were misreading when they were brand new. That is why I question the batteries themselves, not their age when they are losing power. Both brands are AA alkaline and yet one is smaller and the smaller gave wrong readings from day one. The larger is giving correct readings.
Better question might have been, can they actually put as much power in a smaller battery? E.g. AAA batteries have less power than AA or D and are smaller The size always grows with the amount of power. No?
And is it safe to switch? Think you say "yes". Thanks again. I do know about white coat syndrome and agree heartily. :-)
In general, the smaller batteries do not have as much stored energy as the larger ones. The type of chemicals used is different in different types of batteries, so a lithium battery that is the same size as a carbon zinc battery might store more energy, but given the same type of battery in different sizes, yes, larger has more "power." However... a large old battery that is partially discharged might have less than a new fresh smaller one.
Yes, the type of switching you are doing is fine. There are other situations where it might not be correct or safe, but not in this instance.
I could digress into "voltage under load" and discharge curves, and the chemical reactions and reasons for particular voltages, but it would serve no purpose.
In general, the smaller batteries do not have as much stored energy as the larger ones. The type of chemicals used is different in different types of batteries, so a lithium battery that is the same size as a carbon zinc battery might store more energy, but given the same type of battery in different sizes, yes, larger has more "power." However... a large old battery that is partially discharged might have less than a new fresh smaller one.
Yes, the type of switching you are doing is fine. There are other situations where it might not be correct or safe, but not in this instance.
I could digress into "voltage under load" and discharge curves, and the chemical reactions and reasons for particular voltages, but it would serve no purpose.
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@ Hazel
When it comes to reading your blood pressure, find out if your BP meter can remember the last readings.
The best way to get a BP reading is to take 3 readings.
About a minute or so apart.
Then average the last two.
You will find that your BP readings are lower than you think.
But, be aware that you should find out which arm gives you the highest blood pressure reading. Then always use that arm for your readings.
Also take your blood pressure at the same time of the day, when monitoring your BP.
Thank you, Irman. I should have had that thought in my head yesterday when the readings came out impossibly low. I did re-take it half an hour later an it did better. So, probably some carelessness on my part.
Thank you, Harry. These batteries were misreading when they were brand new. That is why I question the batteries themselves, not their age when they are losing power. Both brands are AA alkaline and yet one is smaller and the smaller gave wrong readings from day one. The larger is giving correct readings.
Better question might have been, can they actually put as much power in a smaller battery? E.g. AAA batteries have less power than AA or D and are smaller The size always grows with the amount of power. No?
And is it safe to switch? Think you say "yes". Thanks again. I do know about white coat syndrome and agree heartily. :-)
If they came in the monitor that is an assumption. The units may have been stored for a long time and the batteries weakened over that time.
Better question might have been, can they actually put as much power in a smaller battery? E.g. AAA batteries have less power than AA or D and are smaller The size always grows with the amount of power. No?
The answer depends on what you are calling power. AAA, AA, C, and D batteries are all 1.5 volts, (unless you're talking rechargeables, then they are 1.2 volts). The larger batteries have more capacity (more stored energy), so will last longer compared to AAA or AA in the same device.
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