此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采取“小心駛(shi)得萬年船”的(de)策略，用(yong)(yong)小電(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)，一般(ban)不超過100mA ，這樣電(dian)(dian)(dian)池(chi)充(chong)(chong)到最后，發熱不至(zhi)于太大，從而(er)延長(chang)(chang)電(dian)(dian)(dian)池(chi)壽命(ming)。缺點是充(chong)(chong)電(dian)(dian)(dian)時間(jian)長(chang)(chang)。現(xian)在生產這類(lei)的(de)廠家(jia)，采用(yong)(yong)中電(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)，100～200mA 充(chong)(chong)電(dian)(dian)(dian)時間(jian)大大縮(suo)短，但是以犧(xi)牲電(dian)(dian)(dian)池(chi)壽命(ming)為代(dai)價。傻瓜型(xing)充(chong)(chong)電(dian)(dian)(dian)器只能(neng)用(yong)(yong)時間(jian)來控制充(chong)(chong)電(dian)(dian)(dian)，它只適合于深(shen)(shen)充(chong)(chong)深(shen)(shen)放的(de)五號、七號鎳鎘(ge)、鎳氫(qing)電(dian)(dian)(dian)池(chi)。

    充(chong)(chong)電(dian)(dian)時間(jian)：T = 1.5C/I（ C是(shi)電(dian)(dian)池容量，I是(shi)充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)）例：如果有個1000mAh 的(de)電(dian)(dian)池放在(zai)充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)是(shi)50mA的(de)充(chong)(chong)電(dian)(dian)器(qi)(qi)上(shang)(shang)充(chong)(chong)電(dian)(dian)，充(chong)(chong)電(dian)(dian)時間(jian)就是(shi)30小時。辨認這(zhe)類充(chong)(chong)電(dian)(dian)器(qi)(qi)的(de)方法(fa)：當插上(shang)(shang)電(dian)(dian)源插頭后，充(chong)(chong)電(dian)(dian)指示燈一直(zhi)亮著。街上(shang)(shang)賣(mai)的(de)10～40元(yuan)以(yi)內的(de)均是(shi)這(zhe)種(zhong)充(chong)(chong)電(dian)(dian)器(qi)(qi)。